Rectangular bales are able to maintain their shape by means of a series of parallel extending twine loops, provided lengthwise around the bales. Balers typically use automatic knotters by which e.g. two knots are made on every loop for binding a bale. An example of such a knotter system for a baler is disclosed in EP 1 584 227 in the name of the Applicant, the disclosure of which is included herein by reference. The knotter system disclosed in EP 1 584 227 has the advantage that two consecutive knots can be formed during one operation cycle, without the formation of twine tails.
A problem with the knotter system of EP 1 584 227 is that, in particular for high density balers, the twine loop is not able to resist the high pressure exerted by the bale. When the bale is formed and moved out of the baling chamber, the compressed crops forming the bale will expand resulting in pulling on the twine. If this pressure is such that the twine loop cannot resist this pressure, it will open at the weakest point in the loop. In the case of the twine loop formed with the baler of EP 1 584 227, the weakest point in the loop is the standard knot. This type of knot has the problem that due to the way it is knotted, the twine ends are able to slide with relation to each other when being pulled on at each end. That way, the knot will open up.
When using more expensive twine, the resistance against slipping is improved, due to the structure of the twine. These type of twine have an internal netting structure with small barbs on the fibres of the netting structure. Due to this netting structure with the barbs, the twines will be entangled more in the knot and will thus be able to withstand the pulling force on the twines. However, the resistance against slipping is limited and it was noticed that this expensive twine is no longer capable of withstanding the pulling force when high density bales are being formed with a baler as disclosed in EP 1 584 227.
Another problem which was noticed with the knotter system of EP 1 584 227 is that the fibres of the twines are often damaged. This damage occurs due to the fact that the twines or strands are firmly gripped by a twine holder in the twine disk. The contact between the strands and the twine holder and twine disk, in combination with the pulling of the rotating bill hook will result in the damage of some of the fibres. If some of the fibres are damaged, this location in the twine will be a weaker point in the closed loop. Depending on the strength of the formed knots and the degree of damage of the fibres of the twine, it is very well possible that the twines will break at the point in the loop where the strands were held when forming the knots.
Reference is also made to the BE application filed by the Applicant on 16 Oct. 2012 with the title ‘Knotter system for a baler’, the disclosure of which is included herein by reference. In this application, it was the object of the invention to improve the removal of the second loop knot from the bill hook by maintaining the cutting arm in the extended position after the second rotation of the bill hook. In this application, as is the case with EP 1 584 227, the second knot will be formed as a loop knot, while the first is still a standard knot.
The object of the present invention is to further improve the knotter system of EP 1 584 227 and more in particular to realize a knotting cycle without leaving loose ends while providing two knots with improved resistance against opening of the knot and with a limited damage to the fibres of the twine.